Reflector signal



July 29, 1941. E. P. BONE 2,250,620

REFLECTOR SIGNAL I Original Filed May 9, 1935 4 Sheets-Sheet l ZSnventorJuly 29, 1941.

E. P. BONE REFLECTOR SIGNAL Original Filed May 9, 1935 4 Sheets-Sheet 2ihmentox: 51/022 5 50225 July 29, 1941. E. P. BONE REFLECTOR SIGNALOriginal Filed May 9, 1935 4 Shets-Sheet s attorneys July 29, 1941. E.P. BONE REFLECTOR SIGNAL' Original Filed May 9, 1955 4 Sheets-Sheet 4 w+2 w w Q Q Q 3nnentor attornegs Patented July 29, 1941 UNITED STATESPATENT E, 2,250,620, y

eral Motors Corporation, Detroit, Mich, a cor poration of Delaware ,7

Original application in, 1935, Serial No. 20,593. Divided and thisapplication May 2, 1938,1SerialNo.205,459

6 Claims.

This invention has to do with auto-collimating reflex devices such asare for road signs and signals to return light from a source, such as anautomobile headlight, back to thevicinity of that source so that anyonein that vicinity, for example, the occupants of the automobile, may seethe sign or signal. by the reflected light. Such devices are commonlyused for road signs indicating danger, stop streets, curves, etc., andfor advertising signs, and are also extensively used on vehicles to givean indication to the driver that there is a car ahead even though theusual tail light on'that car be extinguished.

It is essential that such devices. operate throughout a wide angularrange to care for various conditions encountered on the road. Forexample, the car ahead carrying the reflex device may be proceedingaround a curve, going up hill or down, or may be proceeding in a pathparallel but to one side or the other of the following car or the reflexdevice when usedas a sign along the road maybe similarly positioned. Inall of-these positions the reflex device must operate toreturn asufficient amount of light to the eye of the driver to give thenecessary warning. The angular range within which a reflex device mustbe effective is determined by road conditions, and a careful. study ofthese conditions indicates the need for a horizontal angular range offrom 30" to 45 to each side of center combined with a vertical angularrange of from 8 to 12, both above and below the horizontal.

In most cases it will be found ample to provide an angular range of 10up and 10 down and 30 to each the area of the field within which thereflex device must be effective approximately 1200 square degrees. Inevery one of the inflnitenumber of positions; the reflex device mayoccupy within this angular range it must serve to return a suffic'ien'tamount of light to the drivers eye to give the desired signal. In eachand every such'position the reflex device must project back upon thelight source a beam pattern of su-fficient spread to include both thelight source'and the drivers eye. The shape of this pattern will bedetermined primarily by the optical units employed, and the size of thepattern will be determined not. only by theoptical units employed, butalso by'the accuracy in manufacture. The more a'ccuratelythe device ismade, the smaller-will be the pattern. The shape and size of: thepattern projected: by thereflex devicewill also vary with the; angularposition of- "the reflex device, and: so will: the. intensity of thereturned; signal. In the side of center, thereby making :3

commercial manufacture of reflex devices by production methods, it isdesirable to reduce the size of the patternformed by the reflected lightas much as possible in order to have a signal of maximum strength.

range of 1-200 square degrees cares for alloondiditions encountered inpractice, present day de-' vices are customarily designed forapproximately 30 angular range in all directions, giving a total rangeof approximately 2800 square degrees. 7

My improved reflex device may be designed for the same angular range inall directions or for greater range horizontally than Vertically. Whendesigned in the last-named manner it is capable. of producing 'a signalof exceptional brightness andefllciency; In all its embodiments myimproved reflex device is characterized by simplicity, ease ofmanufacture and insensitiveness to inaccuracies unavoidable inmanufacture.

To provide the necessary horizontal angular range I make use of twovertically positioned reflecting surfaces arranged at an angle of 90.Surfaces so arranged will, as is well known, return projected light backto the source throughout a wide horizontal angular range, although withsome reduction in strength of the signal as the angle increases becauseof the fact that 'less light then strikes the device. Such devices,.-however, are ineffective over any substantial vertical angular range forthe reason that-upwardlyor downwardly inclined incident. rays arereflected at opposite vertical angles in accordance with the laws ofreflection from plane surfaces. To overcome this defect I haveemployedmeans tofcondense the rays and bring them to. a horizontal linefocus, the condensedrays impinging on the 90 V reflector and beingreturned in the direction from which they came by'the combined action ofthe reflector and condensing means. By suitably designing the condensingmeans it'is possible to secure the necessary vertical angular range. Thecondensing action may be accomplished'either by'reflection or refractionbut'in the preferred form of the invention the condensing means takesthe form of horizontallcylindrical lenses or. flutes. The 90 V'reflector'ribs'may beformation the oppositevsi'de of the same lass onwhich the lenses or flutes are formed and the reflecting surface may becoated with silver or the like or left uncoated as desired. Thereflecting efl'iciency, will of course, be increased by the coating.Alternatively the 90 V ribs may be formed of metal and may be spacedfrom the horizontal cylindrical lenses or flutes or the horizontalflutes may be formed on the ribs. In any design greatly improvedefficiency will be obtained by so arranging the parts that the rays arebrought to a focus in a line bisecting the 90 With my device superiorperformance may be obtained by designing it to operate effectively onlywithin the angular range. required by road conditions. This makes itpossible to use the necessary optical units to greater advantage thanhas heretofore been possible in reflex devices, and to secure higheraverage efliciency. With reduced vertical range it is possible to employcondensing devices within limits of design within which opticalaberration is substantially negligible. The importance of this will beappreciated when it is realized that optical aberration forces thedesigner of reflex buttons to compromises which constitute the chiefsource of loss of efiiciency in this type of signal.

While the cube corner type of reflex is substantially free from theusual types of optical aberration, it suffers from an equivalent defectin the necessity for an exact angular relation between three reflectingsurfaces, each of which acts upon every reflected ray in succession.Such devices are inherently diificult to manufacture owing to theangular cavities which characterize them. With my improved device buttwo reflecting surfaces are employed and as these take the form ofsimple 90 V grooves they may be more easily made and held within thenecessary limits. i While my device may suffer to some extent from lackof the exact angular relation between the two reflecting surfaces, suchdefect affects the rays in only one plane,.the horizontal; while in thecube corner devices, such defect affects the rays in both horizontal andvertical planes. This advantage, coupled with the fact that mycondensing means is substantially free from aberration throughout thereduced vertical range results in a large increase in the net resultantbrightness.

My reflex devices present many other advantages. The employment of buttwo reflecting surfaces makes it possible to better confine thehorizontal spread to the small amount desired. The V grooves in moldsand dies may be readily machined with a high degree of accuracy and maybe readily cleaned and polished. Other objects and advantages of theinvention will be pointed out in the course of the followingdescription.

Figure 1 is a diagrammatic horizontal section through one form of myinvention.

Figure 2 is a section taken substantially on line M-M of Figure 1,looking toward the left of that figure and showing typical incident raysAB.

Figure 3 is a section taken on the line 3-0 Figure 1; v

Figure 4 'is a section taken substantially on line MM of Figure 1,looking toward the right that ure and showing only the reflected raysCD.

Figures 5 to 8 are views corresponding to Figwas 1 to 4, respectively,but showing th action of the same device with angularly incidenthorizontal rays.

Figures 9 to 12 are a set of views corresponding to Figures 1 to 4,respectively, but showing the action of the device with downwardlyinclined rays.

Figure 13 is a section corresponding to Figure 1, but showing anembodiment of my invention which may be made entirely of glass.

"Figure 14 is a section along line AB of Figure 13 looking toward theleft.

Figure 15 is a section on line BC looking toward the rear, and

Figure 16 is a section on line CD looking toward the right of Figure 13.

Figures 17 to 20 are a set of views corresponding to Figures 1 to 4showing a further modification made of metal.

Figure 21 is a front elevation of a tail lamp showing one way in whichmy invention is embodied.

Figure 22 is a side elevation of Figure 21, showing in part, a verticallongitudinal section. through the tail lamp.

Figure 23 is a horizontal longitudinal section through the same taillamp.

Figure 24 is a front elevation of a portion of a typical commercialembodiment of my invention.

Figure 25 is a section taken on line 25-25 of Figure 24.

Figure 26 is a section taken on line 25 -26 of Figure 24.

Figure 27 is a section similar to Figure 26 showing a modification. a

Figure 28 is a horizontal section through a further modified form.

Figure 29 is a front elevation of a further modification.

Figures 30 and 31 are sections on lines 30-30 and 3I-3| of Figure 29.

Figure 32 is-a section similar to Figure 31 showing an additionalmodification.

Figures 1 to 4 show diagrammatically the operation of one form of myreflex device. Here I indicates a horizontal flute element in the formof'a cylindrical lens and 2 and 3 indicate the-cooperating V reflector.As shown in the horizontal section in Figure 1, ray AB is reflected toCand is again reflected, emerging as ray C-D parallel to the incidentray AB. It will be understood, of course, that the same action takesplace in a reverse direction in'the case of a ray of light incidentalong the path D-C. As shown in Figure 2, the flute I condenses theincident rays on the reflector section 2, and as shown in Figure'3, therays are reflected and brought to a focus at a point in the plane MMwhich bisects the 90 angle of the reflector. The rays thereafterdiverge, striking the reflector section-3, as

indicated at C, whereupon as shown in Figure 4, the rays are'againreflected, diverging outwardly and passing throughthe lens I whichrefracts them into paths parallel to the direction of incidence. It willbe apparent that with the construction shown, the focal length of theflute l is the distance along the central ray from the flute l to B tothe focal point in the bisecting plane M'M.

There is illustrated in Figures 1 to 4, the action of the system on asingle vertical sheet of rays incident parallel to the bisecting planeMM. It will be apparent that with this system each vertical sheet ofrays parallel to the one illustrated will be similarly brought to afocus at a point'in th'ebisecting plane since the distance in thegeneral direction of incidence.

from-the-pointof incidence on; the lens to the point of incidence on thereflectorand thence over tothe medianplane-isthe same for all such rays.All such rays Will, of course, be reflected back in a direction'paralleltothe direction of incidence, just as in the case of the rays AB CD. VIn Fgures5 to 8 there is shown the'a'ction of the system "on horizontalrays'incident in a vertical plane making an angle with the'bisectingplane MM. It'will'be noted that'owingtothe fact that the path of'the'incident rays'is at an angle to the axis of the flute, the flutewill act as a lens of shorter focal length, and this combined with theincreased 'distancefrom A to'B tothe bisecting plane MM along the pathof, the reflected rayswill cause'the focal point to lie to the left ofthe plane M"M with the consequence that, as shown in Figure 8,somefo'fIthe raysreflected from surface Swill .miss the "flute .l.altogether, while those that strike it will emerge at slight'angles toeach other, although in the (general direction ofincidence.v It isapparent from a consideration of these flguresthat the construction issomewhat less eflicient in the case of rays incident at an angle to themedian plane, but such efficiency is still relatively high.

Figures 9'to 12 illustrate the action in the case of rays parallel toplane M-M but incident at anangle with the horizontal. 'As shown'inthese figures owing to the somewhat longer path of travel from thelensto the reflector at B" and thence to the bisecting plane MM, the .rays

much optical aberration with'the resultant'reduction-in- -concentrationof the reflected light. Itis also apparent that if *desired the fluteelements I could 'bedesigned to -produce "a focal "area*rathe'r come toa focus at a point to theleft of themev dian plane so that, as shown inFigure 12, some of the rays miss the lowerend of the flute 1 altogether,while the remainder pass through the lens and issue at slightlydivergent angles, but It be observed, of course, that the efficiency ofthe device, as illustrated, is somewhat less foi' rays incident atvertical angles than for horizontal rays incident parallel to themedian, plane. I

. It will be understood, of course, that in the case .of rays incidentboth at angles to the bisecting plane M--M and to the horizontal, therewill be some of the action shown inFigures 5 to 8' combined with some ofthe action shown in Figures 9 to 12, but, in general, within the rangeof the device there will be a substantial amount of fautocollimation forany such rays incident within the range for which the device isdesigned.

It will be understood, of course, that all 'o'fjthe elements in theabove described construction are subject to design to produce theresults desired.

While it is true that maximum collimation is obtained when the rays .arebrought to a focus in the bisecting plane MM, it may be desirable toemploy flutes l of somewhat greater focal length so as to reduce theefiiciency in the case of rays receivedhead on, but to increase theefliciency in the case of rays incident at an engle. Some suchcompromise in focal lengthwill be found in most cases to givethe mostdesirable operation.

I prefer to employ cylindrical lenses with a focal length substantiallyequal to or slightly more than the maximum distance between :the outsidesurface of the lens and the most remote part of the reflecting surfaces.In the design of these devices it is also important that the height h=2fTan 0/2 "than a line focus, this'being-done with suitable curvesor-combinations of "curves.

In Figures 13 to 16 ther'eis shown a modification in whichthespace-between'the outside of the "flute and the reflector'is filledwith glass. In 'such constructions, of course, the'reflecting surfaces2' 3"1nay be formedby platingdirectly'on the glass if desired. Thisdevice will op- ]erate without aspecial reflecting surfacewithin therange of angles within which substantially total internal reflection isobtainable with the kind of glass employed. In the construction ofFigures '13 to 16 the reflectors 2' 3 =are'also modified in that theytake the form of concave horizontalflutes, as "shown in Figures 14 to16, "so that the focallengtho'f the system is the combinationofthe-'foca1 length of the cylindrical lens or flute l and of thecooperating concave 'flu'te 'on the reflector? "or ,3, In Figure 14, Findicates the focal'length of the flute I assuming that there is-no'change inmedium through which the light pass'es "after entering theglass while F" indicates the focal length of the combinati'on of flutel' and reflector 2:. Owin to reflection'atB the rays illustrated will ofcourse bebrougihttoa focusat F". This construction is subject to "thesame modifications referred to in connectionwith preceding'form. Inaddition, the concave-flutes may be modifled to"cor'r'ect for aberrationas described in connection "with *the next'form, or if p'referredtheymay beomitted altogether. in t 7 I H W I In Figures 1'7 to 20 there isshown a further modification in whi ch'the' only flutes employed are on:the reflecting surfaces 23' The construction illustrated may, of course,be made of metal formed by "stamping, or rolling, or, if desired, couldbe made of glass having one plane surface and the opposite surfaceformedjwith ribs of the configuration'shown in Figures 17 to 20,thesurfaces of the ribs preferably, although not necessarily, being coatedwith metal or otherwise provided with a close fitting metallicreflecting surface. In the construction 'illus 'trated' it will be clearthat the auto collimating action is substantially the same as in theform shown in Figures 1 to 4, Howeveryit is to be noted thatif thereflecting fluteshave the same curvature throughout "their length thelight rays will be brought to focus along lines parallel to the fluteaxes, -such lines intersecting the median plane MM' at a single pointonly. Consequently there will be greater optical aberration with thisconstruction than with theconstructions previously described. Thisobjectionmay, of, course, be overcome by employing reflecting fluteswith focal lengths" that increase with the di'stancefromthe apex of the90refle'ctors of which they form a part. I-Iowever, even-though uniformcurvatures be employed on I the reflect ing elements with some increasein aberration and loss in efliciency, this 'form'of the-invention hasthe advantage of low cost of manufacture, for strips and sheets of thisconfiguration can readily be madeby stamping and rolling at 1st cost.With this form of the invention there is likewise opportunity forvariation in focal length of the reflecting flutes to produce theresults desired. There will likewise be the same dispersion of light inthe case of angularly incident rays, and, in general, the dispersionwill be greater, for assuming the same tolerances and order of errors inboth cases, when a reflecting surface is angularly displaced 1 thereflected ray is displaced 2 from the intended direction, while if a.refracting surface, such as the flute l, of Figures 1 .to 4, isangularly displaced 1, the refracted ray is displaced only approximatelyfrom the direction indicated. Thus, where reflection alone is reliedupon to produce the same bending of rays as can be accomplished whollyby refraction, the tendency-to distortion is approximately five times asgreat. Since in my preferred construction the bending is accomplishedpartially by refraction and partially by reflection, the tendency to.distortion is correspondingly reduced. 1

In Figures 21 to 23 I have shown my invention embodied in an automobiletail lamp. Here It] indicates a lens, the upper part of which may beprovided with the usual Fresnel and catadioptric rings to concentratethe light, while the' lower portion is provided with horizontal flutes12 designed to focus incident light on the reflecting ribs 14. The ribsM as shown in Figure 22 may be provided with focusing flutes to furthercondense the light, or these may be omitted if preferred. Figure 23illustrates the action of the device with head-on andangularly incidentrays. The construction is optically the same as that of Figures 1 to 4,except that the reflecting ribs I4 are fluted as in the forms shown inFigures 13 to 20. The surfaces of the flutes I 2 in this form of theinvention arepreferably corrected so as to overcome optical aberration.These flute surfaces also have sharper curvature from the centeroutwardly both vertically and laterally to obtain shorter focal lengthstoward the edges, to compensate for the varying distamces of the lensfrom the reflector. In this construction, of course, the arrangement ispreferably such that substantially horizontal rays are brought to afocus in a line lying in the median plane. I

An advantage of this construction over the other reflex devices shown isthat the structure can be made on a larger scale so that the mechanicalinaccuracies are not so effective in distorting the reflected light. Thecorrected curvature and other refinements are thereby warranted.- In theusual pressed glassreflex device,

a beam of light several hundred feet long is'controlled on the shortendof a fulcrum, usually only about long. -In-the tail light illustratedthe short end of the lever of the light beam, thatis, thedistancebetween the incident surface of the flute and the focus, alongthe path of a light ray, can be increased to some 2" or so, and as aconsequence the construction is not nearly so sensitive to inaccuraciesin manufacture.

The correction of the curvature of the condensing flutes used in thevarious embodiments of my invention will effect a very considerableincrease in brightness. The principles involved in such correction arebriefly as follows:

The ideal condition for our converging lens obtains when all of the rayscome to atoms in the bisecting plane MM, Figure 1. It is' commonpractice in the design of lenses to use a simple curvature which is acircle in cross section. But with the use of a circle an outside ray,such as the top or bottom ray of Figure 2, strikes the surface of theglass at a greater angle than does the central ray. As a consequence ofthis, the outer rays are refracted more and fall short of the desiredfocus in the plane MM. This discrepancy is usually called sphericalaberration. It may be noted here that most optical surfaces are surfacesof revolution, the circle when revolved, forming a sphere and hence thename spherical aberration. In our case of a cylindrical lens we have thesame effect from our circular cross section although it is not actuallyspherical. V

In the present construction we have aberrations which are additional tospherical aberration but they are all mostly caused by the same generaleffect of the angular rays falling short of the intended focus. Thus,the rays A'B'C'D. from the side angles as shown on Figures 5 to 8, fallfurther short of the plane MM. Also, the rays incident from an upwardangle shown on Figures 9 to 12 have a furthei tendency to fall short ofthe plane MM. More over, in manufacture, the spacing between theconverging means I and the reflector 2, 3, may be inaccurate and causethe point at which the rays tend to focus to miss the plane MMaltogether. The combination of all the above effects which tend to keepthe rays from coming to the intended focus in plane MM, may beconsidered as general optical aberrations. The first mentioned sphericalaberration is only a part of the general aberrations. Sphericalaberration can be completely corrected for by changing the circularcross section to some adapted form of a Cartesian oval such as anellipse or parabola. Such a corrected or aspherical curvature may bringall of the rays A, incident head-on, to a focus in plane MM, asillustrated in Figures 2 and 3. This correction is well known in theart. However, even with this correction, when rays are not head-on butincidentat an angle they again do not come to a precise focus in theplane M M. I preferably make use of a corrected aspherical curvature tobetter correct for aberrations in general from all of the above causesand not merely to correct for spherical aberration. Considering these,my preferred curve is arrived at by mathematical optics. My curve may ormay not be approximated by some simple mathematical curve, such as acircle, parabola or ellipse, but more often is found in some unnamedform.

In Figures 24 to 26 I have shown a commercial embodiment of my inventionas it may be made when pressed out of glass. Optically theconstructionis the same inprinciple as the form shown in Figures 13 to,16 except that the reflecting surfaces indicated at 22 and 23 are freefrom flutes. To secure maximum efliciency the condensing flutes 2|should be given special curvature to correct for optical aberration asabove explained. The thickness of the glass should be maintained withinclose limits to insure that the rays will come to a focus in the planebisecting the angle between the reflector surfaces. A reflecting coatingon the surfaces of the V rib will also increase the efficiency of thedevice as well as greatly increase its angular range.

In Figure 27 I have shown an even more eflicient design, correspondingoptically to that shown in Figures l'to 12, in which the 90 V groovesare formed .in a sheet metal plate 25 secured to the back of the glass27 carrying the condensing flutes or lenses 29 as by spinnin the edgesof themetal about the glass. This constructionlwillbe more efficientbecause a pressed metal reflecting surface may .be readily made freerffrom surface irregularities than a pressed glasss'urface such" as showninFigures 24 to 26. Another advantage of this construction arises fromthe fact that it is not so sensitive to variations'in the thickness ofthe glass since the position of the focus of incident rays is determinedprimarily by the overall distance from the front of the glass to thefront of the reflector rather than by the proportion of the length ofthe path of the rays through glass to the length of the path of the raysthrough the air between the glass and the reflector, and the saidoverall distance may be accurately maintained in assembly.

In Figure 28 I have shown a modification of the construction shown inFigure 26 in that the orientation of the reflecting V ribs is varied.This is of especial advantage when the back of the ribs is not providedwith a reflecting coating for then the horizontal angular range islimited by the failure of the ribs to internally reflect light at thewider angles. By orienting some of the ribs at an angle to normal to theglass they are effective to return light at the wider angles althoughtheir effectiveness in the case of headon or oppositely inclinedincident rays is considerably diminished.

In Figures 29 to 31 I have disclosed an application of my inventionwhich employs reflection only but in which the condensing means is notsuperimposed on the 90 V ribs. Condensing is done by employinghorizontal cylindrical reflecting flutes to bring the incident rays to aline focus. The condensed rays are directed on vertical 90 V ribsarranged in front of the flutes, the ribs acting in conjunction with theflutes to return the rays in the direction of incidence. The cylindricalflutes 30 are preferably formed by stamping a sheet of metal indicatedat 3|, and the 90 V ribs are formed by suitably stamping narrow stripsof metal indicated at 32. The strips 32 are secured to the sheet 3| byriveting as indicated at 34, or in any other suitable manner. The flutesand ribs are preferably so spaced that the condensed rays are brought toa focus in the plane bisecting the angles of the ribs so as to givemaximum efliciency.

It will be noted by reference to Figure 31 that the strips 32 present 90reflecting surfaces on their outer sides as well as on their inner sidesso that if the outer surface is silvered it will of itself act as asimple 90 V reflex device with respect to normally incident rays. As inthe other forms of my invention the vertical angular range of thisreflex device may be increased by placing a horizontal condensing flutein front of it as in the form shown in Figures 1 to 4.

Instead of making the strips of 90 V ribs out of sheet metal they may beformed upon a cover glass as indicated at 32' in Figure 32, preferablybeing silvered to give the necessary high reflecting efliciency. Betweenthe strips the glass of course should be plane.

For best results the radius of curvature of the cylindrical flutes 30should be approximately twice the distance from the 90 V ribs to theapex of the flutes, and the width of the flutes should be approximatelythree times the width of the V ribs.

It will be understood that my invention is capable of considerablemodification in addition to those illustrated. The reflex devices may bedesigned for the range of angularity desired, and

be found desirable to make the devices as "steam rately as" ispossibleiin .large production. tol 'secure maximumiefflcieney. j i

While I'have'empha'sized the usefulness'of my reflex device for roadservice and have emphasized different lateral and vertical angularranges it will be appreciated that it may be used for other purposes inwhich other angular ranges may be desired. Thus it may be readilyemployed for greater vertical range than horizontal range by simplyrotating it 90.

It will be understood, therefore, that the terms vertical and horizontalas used in this specification are to be construed in a relative senseand not in an absolute sense.

It is possible that in some uses it may be desirable to depart from anangle of exactly 90 between the condensing flutes and the V ribs to varythe field within which the device is effective, although with someslight loss in efficiency, and all such modifications come within thescope of my invention.

This application is a division of my copending application Serial No.20,593, filed May 9, 1935 for Reflector signal.

I claim:

1. An auto-collimating device comprising a pair of substantiallyvertically extending reflecting surfaces arranged at substantially rightangles to each other, said surfaces being formed to provide horizontalconcave flutes having axes lying in the same plane to condense theincident parallel light rays, said flutes being shaped to bring incidentlight to a focus between said surfaces.

2. An auto-collimating reflector comprising a pair of substantiallyvertically extending metallic reflecting surfaces arranged atsubstantially a right angle to each other, said surfaces being formed toprovide horizontal flutes to condense incident parallel light rays andfocus the same in the vertical plane substantially midway between saidsurfaces.

3. An auto-collimating reflector comprising a pair of substantiallyvertically extending metallic reflecting surfaces arranged atsubstantially a right angle to each other and metallic horizontallyextending concave portions operatively associated with said reflectingsurfaces, said concave portions being arranged to condense incidentparallel light rays and bring the same to a focus in a vertical planebetween said reflecting surfaces.

4. An auto-collimating reflector comprising a pair of verticallyextending metallic reflecting surfaces arranged at substantially a rightangle to each other and horizontally extending concave metallic membersassociated with said vertically extending reflecting surfaces, saidconcave members being arranged to condense incident parallel light raysand bring the same to a focus in a vertical plane between saidreflecting surfaces.

5. An auto-collimating device comprising a pair of substantiallyvertically extending metallic reflecting surfaces arranged atsubstantially a right angle to each other, said surfaces being formed toprovide horizontal concave flutes lying in the same plane to condenseincident parallel light rays, said flutes being shaped to bring incidentparallel light rays to a focus in a. vertical plane substantially midwaybetween said surciated with said vertically extending metallic surfaces.faces, said concave portions being arranged to con- 6. Anauto-collimating device comprising a dense incident parallel light raysand bring the pair of substantially vertically extending metalsame to afocus in a. vertical plane substantially lic reflecting surfacesarranged at substantially 5 midway between said reflecting surfaces.right angles to each other and metallic horizontally extending concaveportions operatively asso- EVAN P. BONE.

